This invention relates to microelectronic devices and fabrication methods therefor, and more particularly to two electrical terminal silicon carbide devices, such as light activated silicon carbide thyristors, and manufacturing methods therefor.
Silicon carbide thyristors are described, for example, in U.S. Pat. No. 5,539,217 (the ""217 patent) the disclosure of which is incorporated herein by reference as if set forth fully. The thyristors described in the ""217 patent are three terminal devices having a gate and one of an anode or a cathode on a first side of the device and the other of the anode and the cathode on the opposite side of the device. Such silicon carbide thyristors may exhibit improved power handling capabilities over similar silicon thyristors.
Light-activated thyristors having an integrated light source and a silicon carbide active layer have been described in U.S. Pat. No. 5,663,580. Such devices may include four terminal devices and include anode and cathode terminals for a light emitting diode which acts to trigger a thyristor having its own anode and cathode terminals.
Silicon thyristors which are light activated have been utilized in high power applications. For example, optically triggered parallel lateral thyristors are described in U.S. Pat. No. 4,779,126.
While silicon carbide thyristors may provide improved power handling capabilities over comparably sized silicon devices, it may be difficult to create large scale thyristors in silicon carbide. For example, in silicon a single thyristor may be made on a wafer such that the thyristor is substantially the same size as the wafer. However, manufacturing defect free silicon carbide wafers may be difficult, if not impossible. Thus, a device which consumes an entire wafer may have defects incorporated into the device which may limit its performance.
Embodiments of the present invention provide light-activated silicon carbide thyristors and methods of fabricating light-activated silicon carbide thyristors. In particular embodiments of the present invention, a first layer of silicon carbide having a second conductivity type is provided on a silicon carbide substrate having a first conductivity type. A first region of silicon carbide having the first conductivity type is provided on the first layer of silicon carbide opposite the substrate. A second region of silicon carbide having the second conductivity type is provided on the first region of silicon carbide opposite the first layer of silicon carbide and is configured to expose a portion of the first region of silicon carbide to light from a light source external to the silicon carbide thyristor so as to provide a light-activated gate region. A first electrode is provided on the second region of silicon carbide and a second electrode is provided on the silicon carbide substrate.
In further embodiments of the present invention, a second layer of silicon carbide is disposed between the silicon carbide substrate and the first layer of silicon carbide. The second layer of silicon carbide has the first conductivity type.
In additional embodiments of the present invention, a second layer of silicon carbide is disposed between the silicon carbide substrate and the first layer of silicon carbide. The second layer of silicon carbide is of the second conductivity type and has a carrier concentration greater than a carrier concentration of the first layer of silicon carbide.
In particular embodiments of the present invention, the first region of silicon carbide forms a mesa. In such embodiments, a third region of first conductivity type silicon carbide may be provided in the first layer of silicon carbide outside of the mesa formed by the first region of silicon carbide so as to provide a junction termination extension.
In still further embodiments of the present invention, a third region of silicon carbide having the first conductivity type is provided in the exposed portion of the first region of silicon carbide. Such a third region of silicon carbide may have a carrier concentration greater than a carrier concentration of the first region of silicon carbide.
Furthermore, the second region of silicon carbide may be configured to expose a pinwheel-shaped portion of the first region of silicon carbide to light from a light source external to the silicon carbide thyristor so as to provide a light-activated gate region having a pinwheel configuration. Alternatively, the second region of silicon carbide may be a plurality of fingers configured to expose a corresponding plurality of finger portions of the first region of silicon carbide to light from a light source external to the silicon carbide thyristor so as to provide a light-activated gate region interdigited with the second region of silicon carbide.
In further embodiments of the present invention, a silicon carbide thyristor, is provided having a silicon carbide substrate having a first conductivity type and a first layer of silicon carbide on the silicon carbide substrate and having a second conductivity type. A first region of silicon carbide having the first conductivity type is provided on the first layer of silicon carbide opposite the substrate. A second region of silicon carbide having the second conductivity type is also provided on the first region opposite the first layer. The first and second regions of silicon carbide are configured to expose a portion of the first layer of silicon carbide to light from a light source external to the silicon carbide thyristor so as to provide a light-activated gate region. A first electrode is provided on the second region of silicon carbide and a second electrode is also provided on the silicon carbide substrate.
In additional embodiments of the present invention, a second layer of silicon carbide is disposed between the silicon carbide substrate and the first layer of silicon carbide and having the first conductivity type. Furthermore, a third region of silicon carbide having the second conductivity type may be provided in the exposed portion of the first layer of silicon carbide and may have a carrier concentration greater than a carrier concentration of the first layer of silicon carbide.
In still further embodiments of the present invention, the first and second regions of silicon carbide are configured to expose a pinwheel-shaped portion of the first layer of silicon carbide to light from a light source external to the silicon carbide thyristor so as to provide a light-activated gate region having a pinwheel configuration. Alternatively, the first and second regions of silicon carbide may be a plurality of fingers configured to expose a corresponding plurality of finger portions of the first layer of silicon carbide to light from a light source external to the silicon carbide thyristor so as to provide a light-activated gate region interdigited with the first and second regions of silicon carbide.
In certain embodiments of the present invention, in the first conductivity type is n-type conductivity silicon carbide and the second conductivity type is p-type conductivity silicon carbide. In other embodiments of the present invention, the first conductivity type is p-type conductivity silicon carbide and the second conductivity type is n-type conductivity silicon carbide.
In additional embodiments of the present invention, a light-activated silicon carbide thyristor is provided by a plurality of light-activated silicon carbide thyristor cells on at least a portion of a silicon carbide wafer, the light-activated silicon carbide thyristor cells having corresponding gate regions at a first face of the silicon carbide wafer that are configured to be exposed to light from a light source external to the thyristor cells and first contacts on the first face of the silicon carbide wafer and a second contact on a second face of the silicon carbide wafer opposite the first face. A connecting plate electrically connects the first contacts of ones of the plurality of silicon carbide thyristor cells.
In particular embodiments of the present invention, only selected ones of the plurality of light-activated silicon carbide thyristor cells are electrically connected by the connecting plate. In such embodiments, the selected ones of the plurality of light-activated silicon carbide thyristor cells may be silicon carbide thyristor cells having a blocking voltage greater than a predefined voltage value. Furthermore, the selected ones of the plurality of light-activated silicon carbide thyristor cells may have a first contact which extends a greater distance from the corresponding gate region than a first contact of other ones of the plurality of light-activated silicon carbide thyristor cells which are not selected such that the connecting plate only contacts the first contact of the selected ones of the plurality of light-activated silicon carbide thyristor cells. Alternatively, the selected ones of the plurality of light-activated silicon carbide thyristor cells may have a first contact. Other ones of the plurality of light-activated silicon carbide thyristor cells which are not selected do not have a first contact so that the connecting plate only electrically connects the selected ones of the plurality of light-activated silicon carbide thyristor cells.
Furthermore, the plurality of light-activated thyristor cells may include any of the embodiments described above. For example, the cells may be provided by a silicon carbide substrate having a first conductivity type and a first layer of silicon carbide on the silicon carbide substrate and having a second conductivity type. A plurality of first regions of silicon carbide having the first conductivity type are provided on the second layer of silicon carbide and a plurality of second regions of silicon carbide having the second conductivity are configured to expose a portion of corresponding ones of the plurality of first regions of silicon carbide to light from a light source external to the silicon carbide thyristor cells so as to provide a plurality of light-activated gate regions. A plurality of electrodes are provided on corresponding ones of the second regions of silicon carbide and an electrode is provided on the silicon carbide substrate, opposite the first layer of silicon carbide. Other of the embodiments described above may also be utilized as the thyristor cells.
In additional embodiments of the present invention, a silicon carbide thyristor is fabricated by forming a plurality of light-activated silicon carbide thyristor cells on at least a portion of a silicon carbide wafer. The light-activated silicon carbide thyristor cells have corresponding gate regions configured to be exposed to light from a light source external to the thyristor cells and first contacts on a first side of the plurality of silicon carbide thyristors cells having the corresponding gate regions and a second contact. The plurality of light-activated silicon carbide thyristor cells are electrically tested to select ones of the plurality of light-activated silicon carbide thyristor cells which pass an electrical test. The first contact of the selected ones of the plurality of light-activated silicon carbide thyristor cells are then selectively interconnected.
Such a selective interconnection may be provided, in further embodiments of the present invention, by selectively depositing contact material to provide a first contact for the selected ones of the plurality of light-activated silicon carbide thyristor cells and electrically connecting the deposited contact material. In such embodiments, the deposited contact material may provide first contacts on the selected ones of the plurality of light-activated silicon carbide thyristor cells such that corresponding first surfaces of the first contacts for the selected ones of the plurality of light-activated thyristor cells are substantially coplanar and extend beyond corresponding surfaces of contacts of the ones of the plurality of light-activated silicon carbide thyristor cells which are not selected. The electrical connection may be made by contacting an electrically conductive connecting plate with the first surfaces of the first contacts of the selected ones of the plurality of light-activated silicon carbide thyristor cells. The selective deposition of contact material may, for example, be provided by masking contact regions of ones of the plurality of light-activated silicon carbide thyristor cells which are not selected and depositing contact material so as to provide the first contacts on contact regions of the selected ones of the plurality of light-activated thyristor cells which are not masked.
In still further embodiments of the present invention, the first contacts may be selectively interconnected by depositing contact material to provide first contacts for corresponding ones of the plurality of light-activated silicon carbide thyristor cells. Contact material is removed from ones of the plurality of light-activated silicon carbide thyristor cells such which are not selected and the deposited contact material interconnected for the selected ones of the plurality of light-activated silicon carbide thyristor cells. The removal of the contact material may be provided by removing the contact material such that corresponding first surfaces of the first contacts for the selected ones of the plurality of light-activated thyristor cells are substantially coplanar and extend beyond corresponding surfaces of the first contacts of the ones of the plurality of light-activated silicon carbide thyristor cells which are not selected. An electrically conductive connecting plate which is contacted with the first surfaces of the first contacts of the selected ones of the plurality of light-activated silicon carbide thyristor cells may electrically connected the first contacts of the selected ones of the plurality of light-activated thyristor cells.
Removal of the contact material may be accomplished by, for example, masking the first contacts of selected ones of the plurality of light-activated silicon carbide thyristor cells and etching the first contacts of ones of the first contacts of the ones of the plurality of light-activated silicon carbide thyristor cells which are not masked.